NonStop Server for Java Programmer's Reference (NSJ 4.0+)

NonStop system. A summary of garbage collector implementations appears in the table below. Paragraphs
that follow discuss various implementations to help you understand performance issues.
Collector Type Implementation Status
Copying collector
Default collector for the young
generation
Mark-sweep collector
Default collector for the tenured
generation
Parallel collector
Disabled
Concurrent low-pause
collector
Disabled
Incremental low-pause
collector
Allowed
Parallel Collector
The parallel collector (or throughput collector) uses the parallel version of the young generation collector.
The parallel collector is disabled in NonStop Server for Java 4 for performance reasons. On the
NonStop system, which has non-preemptive threads, the parallel collector does not perform as well as the
default collector because of overhead (such as synchronization) associated with the parallelism.
The following java command options that specify a parallel collector or apply to a parallel collector are not
valid for NonStop Server for Java 4:
-XX:+UseParallelGC
Specifies a parallel garbage collector. If you specify this option, the Java VM exits with the error:
-XX:+UseParallelGC option is not supported on this platform.
-XX:+UseParNewGC
Specifies a parallel garbage collection. This option is disabled. If you specify this option, the Java VM
exits with the error: -XX:+UseParNewGC option is not supported on this platform.
-XX:+UseAdaptiveSizePolicy
Specifies an adaptive size policy. This option applies only for a parallel collector and, therefore, is
disabled. If you specify this option, the Java VM exits with the error:
-XX:+UseAdaptiveSizePolicy option is not supported on this platform.
-XX:+AggressiveHeap
Obtains the platform resources and configures the heap layout accordingly, uses parallel collector, and
enables AdaptiveSizePolicy option. This option applies only for a parallel collector and,
therefore, is disabled. If you specify this option, the Java VM exits with the error:
-XX:+AggressiveHeap option is not supported on this platform.
Concurrent Low-Pause Collector
A concurrent low-pause collector is for tenured generation. This collector does most of the collection
concurrently with the application execution. This collector divides the collection into different phases and
does some phases concurrently with the application execution and others in "stop the world" mode. This